1. Field of the Invention
The present invention relates to an information recording/reproducing apparatus such as an optical disc driving apparatus or an audio/video tape recorder which uses a cartridge internally holding an information recording medium.
2. Description of the Prior Art
As is represented by the lap-top type computer, when a conventional information recording/reproducing apparatus using a cartridge internally holding an information recording medium is to be built in a compact housing, a critical problem arises in making the structure thin.
Conventionally, an opto-magnetic disc apparatus focuses a light beam on an optical disc (which is substantially the information recording medium) held inside of a cartridge through a window provided in the lower surface of the cartridge in order to generate an easily-magnetizable condition by locally raising the temperature above the curie-point, and then records information by generating a magnetization of the optical disc in correspondence with a magnetic field generated by an electromagnet, or a permanent magnet, or a magnetic head installed in a position facing the optical disc through a window provided in the upper surface of the cartridge opposite to the lower surface of the optical disc.
A mechanism related to the above is illustrated in a Japanese publication "Information Processing", Vol. 26, No. 1, page 27, FIGS. 2 and 3. Reading of the recorded information is executed by detecting an inversion of magnetization caused by the "Car effect", which causes the polarized plane of said beam reflected by the information recording medium to rotate itself in response to the magnetization.
Nevertheless, in order to invert a magnetic field at a very fast speed in a process of forming a sufficient magnetic field by using a coiled electromagnet, it is essential for the system to solve problems of the delayed rise of current and heat generation, and thus, actually, formation of a thin structure cannot easily be achieved. Further, when the magnetic field is inverted by a high speed inversion of a permanent magnet, which has a relatively large size for generating a high density of magnetic flux, a substantial rotation space is needed for the permanent magnet to invert, and thus it is difficult to achieve a thin structure. Furthermore, when transferring the magnetic head at a very fast speed synchronous with the transfer of the optical beam spot, it is essential for a support for the magnetic head to have an extremely rigid structure in order to precisely hold its own resonance and relative position to the optical disc, and thus it is quite difficult to make the support thin to achieve a thin structure.
Regarding an optical disc driving apparatus which is substantially an information recording/reproducing apparatus as well, a method is employed for securing the optical disc to the disc table for rotating the optical disc, in which a disc clamper is set in a position opposite to the disc table across the optical disc and a permanent magnet is provided on either the disc table or the disc clamper, whereas a ferromagnetic substance is provided on the opposite side in order to secure the optical disc to the disc table by applying the mutual attractive force. However, the optical disc must be securely clamped when increasing the signal-transfer rate generated by rotating the optical disc at an extremely fast speed. Since the permanent magnet or ferromagnetic substance needs sufficient thickness, provision of a thin structure for the conventional apparatus is a critical problem.
On the other hand, in order to transfer the electromagnet or the disc clamper facing the optical disc to a predetermined position after loading the cartridge internally holding the optical disc inside of the information recording/reproducing apparatus, a mechanism for implementing interlocking movement is needed for operating the optical disc driving apparatus. For this purpose, a rotary cam device is conventionally used which repeatedly moves those members connected to the cam follower by transferring the cam follower by rotating it along the shape of the cam. To transfer a plurality of cam followers in different directions and/or different distances from each other, a plurality of rotary cams connected to each other via gears are provided, or a plurality of cam-shaped grooves or projections corresponding to the expanded outer diameters of the rotary cams are provided. Although achievement of a compact and thin structure of the rotary cam is required, actually it is very difficult for any conventional information recording/reproducing apparatus to have a compact and thin structure where a plurality of rotary cams or rotary cams having a large outer diameter for transferring a plurality of cam followers are used.